It seems to me undeniable that up to this century literature used language in the way we all use it, painting represented what anyone with normal vision sees, and music was an affair of nice noises rather than nasty ones. The innovation of “modernism” in the arts consisted of doing the opposite. I don’t know why, I’m not a historian. You have to distinguish between things that seemed odd when they were new but are now quite familiar, such as Ibsen and Wagner, and things that seemed crazy when they were new and seem crazy now, like Finnegans Wake and Picasso.